Known treating agents for heart diseases, e.g., angina pectoris, myocardial infarction, and heart failure, include .beta.-blockers, calcium blockers, and cardiotonics.
Drugs having serotonin 2-receptor antagonistic activity have recently been studied as treating agents for the heart diseases, but there has been found no drug having sufficient effects.
Serotonin has strong physiological activities, such as blood platelet aggregation and vasoconstriction, and is a neurotransmitter. Serotonin is known to act serotonin receptors, and the serotonin receptors are known to include serotonin 1-receptor, serotonin 2-receptor, etc. In case of cardiac infarction endothelial cells of coronary vessels are injured and in such case it is considered that serotonin causes vasoconstriction or thrombus formation through serotonin 2-receptor, resulting in further reduction of blood supply to the ischemic site of the myocardium. From this point of view, drugs for treating ischemic heart diseases have also been studied.
As a representative serotonin 2-receptor antagonist which has been clinically used, Ketanserin is known. Also, Ritanserin and Irindalone are known as serotonin 2-receptor antagonists but they are not yet practically used in therapy.
Ketanserin is a serotonin 2-receptor antagonist and also strong .alpha..sub.1 -receptor antagonist, and hypotensive activity thereof is believed to be attributed to the .alpha..sub.1 -receptor antagonistic activity On the other hand, strong hypotensive activity is unfavorable for some ischemic heart diseases, such as acute myocardial infarction. From this viewpoint, Ketanserin having strong .alpha..sub.1 -receptor antagonistic activity is not useful for the treatment of ischemic heart diseases.
From the same reason, Irindalone having strong hypotensive activity due to .alpha..sub.1 -receptor antagonistic activity is also unfavorable.
While Ritanserin shows weak .alpha..sub.1 -receptor antagonistic activity, it is known to have a neuroleptic activity and is therefore an unsuitable drug for circulatory diseases.
Thus, most conventional serotonin 2-receptor antagonists have many pharmacological activities such as .alpha..sub.1 -receptor antagonistic activity and neuroleptic activity other than the objective activity.